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At least 289 records · Page 16Linked to original sources
PubMed1995

Optic neuritis with silent cerebral lesions: availability of FLAIR sequences.

A 10-year-old male suffering from acute optic neuritis is reported with multiple silent cerebral lesions, which remained visible only with fluid-attenuated inversion recovery sequences at 3-week intervals. Conventional sequences with magnetic resonance imaging did not visualize the lesions. Fluid-attenuated inversion recovery sequences are highly sensitive for the detection of silent lesions in acute optic neuritis.

Brain↗
PubMed1998

Triple helices formed at oligopyrimidine*oligopurine sequences with base pair inversions: effect of a triplex-specific ligand on stability and selectivity.

Oligonucleotide-directed triple helix formation is mostly restricted to oligopyrimidine*oligopurine sequences of double helical DNA. An interruption of one or two pyrimidines in the oligopurine target strand leads to a strong triplex destabilisation. We have investigated the effect of nucleotide analogues introduced in the third strand at the site opposite the base pair inversion(s). We show that a 3-nitropyrrole derivative (M) discriminates G*C from C*G, A*T and T*A in the presence of a triplex-specific ligand (a benzo[e]pyridoindole derivative, BePI). N6-methoxy-2,6-diaminopurine (K) binds to an A*T base pair better than a T*A, G*C or C*G base pair. Some discrimination is still observed in the presence of BePI and triplex stability is markedly increased. These findings should help in designing BePI-oligonucleotide conjugates to extend the range of DNA sequences available for triplex formation.

Chromosome Inversion↗
PubMed1998

Use of fluid-attenuated inversion recovery (FLAIR) pulse sequences in perinatal hypoxic-ischaemic encephalopathy.

The purpose of this study was to evaluate the usefulness of fluid-attenuated inversion recovery (FLAIR) techniques in patients with perinatal hypoxic-ischaemic encephalopathy. 13 patients with a history of perinatal hypoxic-ischaemic encephalopathy (age range 1 month to 3.6 years) underwent T1 and T2 weighted spin echo and FLAIR imaging with a 1.5 T superconducting unit. FLAIR images were qualitatively evaluated in comparison with T1 and T2 weighted images by three experienced radiologists. Quantitative analysis (contrast and contrast-to-noise ratio) was also performed. FLAIR images were preferred to T1 and T2 weighted images in the demonstration of periventricular leukomalacia (PVL), cystic PVL and subcortical lesions near the brain surface. On T1 and T2 weighted images, almost all lesions were demonstrated as hypointense or hyperintense areas, respectively. However, FLAIR images could differentiate cystic lesions by their signal intensities. FLAIR images were not diagnostic in two cases with PVL. In conclusion FLAIR sequences provide useful information in patients with perinatal hypoxic-ischaemic encephalopathy.

Child, Preschool↗
PubMed2002

DNA sequence analysis of interlocus recombination between the human T-cell receptor gamma variable (GV) and beta diversity-joining (BD/BJ) sequences on chromosome 7 (inversion 7).

V(D)J recombinase-mediated recombination between the T-cell receptor (TCR) gamma variable (GV) genes at chromosome 7p15 and the TCR beta joining (BJ) genes at 7q35 leads to the formation of a hybrid TCR gene. These TCR gamma/beta interlocus rearrangements occur at classic V(D)J recombination signal sequences (RSS) and, because the loci are in an inverted orientation, result in inversion events that are detectable in the chromosome structure as inv(7)(p15;q35). Similar rearrangements involving oncogenes and either TCR or immunoglobulin genes mediated by the V(D)J recombinase are found in lymphoid malignancies. Oligonucleotide primers that allow polymerase chain reaction (PCR) amplification across the inv(7) genomic recombination junction sequence have been described. Southern blot analysis has been primarily used to confirm the GV/BJ hybrid nature of the product, with limited information on the DNA sequence of these recombinations. We have modified this PCR method using total genomic DNA from the mononuclear cells in peripheral blood samples to increase specificity and to allow direct sequencing of the translocation junction that results from the recombination between the GV1 and BJ1 families of TCR genes in 25 examples from 11 individuals (three adults, one child, six newborns, and one ataxia telangiectasia (AT) patient). We focused on samples from newborns based on previous studies indicating that the predominant hypoxanthine-guanine phosphoribosyl transferase (HPRT) mutations in newborns are V(D)J recombinase-mediated deletion events and that the frequency of these mutations decreases with increasing age. Although the dilution series-based PCR assay utilized does not yield sharply defined quantitative endpoints, results of this study strongly suggest that inv(7) recombinations in newborns occur at equal or lower frequencies than those seen in adults. Consistent with the PCR primer pairs, all sequenced products contain a GV1 and a BJ1 segment and most also contain a BD1 segment. GV1s2 and 1s4 were the most frequently found GV1 genes (8 and 9 examples, respectively) and BJ1s5 and 1s6 were the most frequently found BJ1 genes (9 and 10 examples, respectively). These results demonstrate the effectiveness of this methodology for assessing GV/BJ interlocus rearrangements mediated by V(D)J recombinase.

Adult↗
PubMedDate not supplied

Fast T2-weighted liver MR imaging: comparison among breath-hold turbo-spin-echo, HASTE, and inversion recovery (IR) HASTE sequences.

BACKGROUND: To evaluate the diagnostic efficacy of fast T2-weighted magnetic resonance (MR) imaging sequences on image quality, hepatic lesion detection, and lesion conspicuity. METHODS: Three breath-hold, fast T2-weighted sequences with turbo-spin-echo (TSE), half-Fourier acquisition single-shot TSE (HASTE), and inversion recovery (IR) HASTE techniques were examined for 43 lesions in 20 consecutive patients. Evaluation was performed qualitatively on image quality and lesion detectability and quantitatively on lesion conspicuity by using lesion/liver signal-intensity and contrast-to-noise ratios. RESULTS: Artifacts were significantly less present on the HASTE sequence (p < 0.01). Both TSE and HASTE sequences detected 39 lesions (91% each); the IR HASTE sequence detected 37 (86%). IR HASTE sequence showed a significantly higher signal-intensity ratio than did the others (p < 0.01). CONCLUSIONS: Breath-hold TSE versus breath-hold HASTE or IR HASTE is still the most robust sequence in lesion detection, image quality, and lesion conspicuity. However, the HASTE sequence offers good lesion detection and image quality, and the IR HASTE has a better signal-intensity ratio.

Adolescent↗
PubMed1990

[Short TR--short TE and UTSS sequences compared in a NMR study of focal neoplastic pathology in the liver].

From December 1987 to January 1989, 66 patients were studied by liver MR imaging: 38 of them were found to have liver tumors, and 28 were studied as a control group. The authors' purpose was to compare the diagnostic accuracy of 0.5 T MR imaging to that of other techniques (CT and US), using mixed Spin-Echo and Inversion Recovery sequences (UTSS). Spin-Echo sequences were used first, with very short repetition times (TR 260, TE 20). Mixed sequences (UTSS) followed, both T1-weighted, lasting 12' and 13' respectively, and then T2-weighted Multiecho sequences lasting 9'. T1-weighted Inversion Recovery sequences provided with good contrast between normal and neoplastic parenchyma, and demonstrated all the lesions shown by other techniques. UTSS proved to be the most sensitive sequence in exactly defining the lesion and its relationship to hepatic vessels. Signal characteristics of T2-weighted Multiecho sequences allowed some neoplastic types to be distinguished that were found to have a particular behavior, especially hemangiomas. T1 and T2 maps were used to characterize the different lesions.

Adenoma↗
PubMed2005

The reproducibility of left ventricular volume and mass measurements: a comparison between dual-inversion-recovery black-blood sequence and SSFP.

The aim of this study was to compare a dual-inversion-recovery black-blood (BB) magnetic resonance imaging (MRI) sequence with steady-state free precession (SSFP) for the assessment of left ventricular parameters. The improved endocardial border definition seen with SSFP was not observed at the epicardial border. Improvements in segmentation at the left ventricular epicardial border have been observed with this black-blood sequence. Left ventricular (LV) mass and LV end-diastolic volume (EDV) measurements as well as inter-observer and intra-observer variability were compared between images acquired with a dual inversion BB and SSFP sequence. The mean+/-1 standard deviation (SD) for LV EDV was 178.3+/-52.7 ml measured with SSFP and 158.8+/-62.2 ml with BB. This difference was not statistically significant (p=0.22). For SSFP, the mean value of LV mass was 124.0+/-27.0 g and 147.5+/-37.4 g for BB, a statistically significant difference (p<0.0001). The dual-inversion-recovery BB imaging showed improved reproducibility for LV mass measurements compared with SSFP and improved spatial resolution. For studies requiring LV mass measurements, the dual-inversion-recovery BB sequence offers improved spatial resolution and improved reproducibility to SSFP.

Adult↗
PubMed1981

Nucleotide-sequence heterogeneity and sequence rearrangements in influenza virus cDNA.

Double-stranded cDNA has been synthesized from influenza virus RNA and cloned into derivatives of the bacteriophage M13 for sequence analysis. The characterization of over 200 clones has permitted an analysis both of nucleotide sequence heterogeneity and of clones containing unusual rearrangements of sequence. Heterogeneity, due to genetic variability in the RNA population and to in vitro synthetic errors, was detected at the low level of one nucleotide difference per 3 700 nucleotides. By contrast, gross sequence rearrangements were identified in eight clones. Inversions of sequence within the same cDNA molecule were the predominant type of rearrangement, and three mechanisms for producing such inversions are discussed. In addition, we observed rarer clones containing sequence from one RNA molecule joined to that from another molecule.

Base Sequence↗
PubMed2004

Protoneus-sequence: extended fluid-attenuated inversion recovery MR imaging without and with contrast enhancement.

Fluid-attenuated inversion recovery imaging (=flair imaging) is widely used as primary screening sequence in various investigation protocols, due to its high lesion contrast and sensitivity in detection of parenchymatous and leptomeningeal disease. An additional increase of sensitivity for detection of lesions may be achieved by contrast-enhanced flair imaging. Based on flair imaging a dual-echo inversion recovery imaging sequence (=proton echo usage [=protoneus] - sequence) was developed, which could significantly extend the possibilities of conventional flair imaging.

Brain Neoplasms↗
PubMed2006

Breakpoint structure reveals the unique origin of an interspecific chromosomal inversion (2La) in the Anopheles gambiae complex.

Paracentric chromosomal inversions are major architects of organismal evolution and have been associated with adaptations relevant to malaria transmission in anopheline mosquitoes. The processes responsible for their origin and maintenance, still poorly understood, can be illuminated by analysis of inversion breakpoint sequences. Here, we report the breakpoint structure of chromosomal inversion 2La from the principal malaria vector Anopheles gambiae and its relatives in the A. gambiae complex. The distal and proximal breakpoints of the standard (2L+a) arrangement contain gene duplications: full-length genes and their truncated copies at opposite ends. Intact genes without pseudogene copies in the alternative arrangement (2La) imply that 2L+a is derived and was viable despite damage to genes, because duplication preserved gene function. A unique origin for the interspecific 2La inversion was challenged previously by indirect genetic evidence, but breakpoint sequences determined from members of the A. gambiae complex strongly suggest their descent from a single event. The derived position of 2L+a, long considered ancestral in this medically important group, has significant implications for the phylogenetic history and the evolution of vectorial capacity in the A. gambiae complex.

Animals↗
PubMed1986

Image contrast and pulse sequences in urinary tract magnetic resonance imaging.

Since image contrast in urinary tract proton magnetic resonance imaging (MRI) depends on both intrinsic properties of the imaged tissue and the imaging technique, it is important to understand the principles underlying image production, both while performing urinary tract MRI and when interpreting the images. This paper reviews briefly the major characteristics of tissue that can produce image contrast: mobile proton density, tissue motion, and relaxation times. It also describes the principles by which these factors, together with the choice of pulse sequence, affect image appearance. The specific pulse sequences described include the spin-echo and inversion recovery sequences; the influence of repetition time, echo delay, and inversion time are also described. Although empiric data regarding the best pulse sequences to use for all types and sites of pathology in the urinary tract are not complete, knowledge of the characteristics of normal tissue and the major sorts of pathologic change permit one to make general conclusions about the appropriate choice of pulse sequences.

Humans↗
PubMed1986

[Magnetic resonance tomography of focal hepatic lesions using the para-magnetic contrast medium, gadolinium DTPA. First clinical results].

The use of the para-magnetic contrast medium gadolinium DTPA for magnetic resonance tomography of focal lesions in the liver was investigated in 31 patients. Two dosage schedules of the contrast medium (0.1 and 0.2 mmol/kg body weight were used with field strengths of 0.35 and 0.5 Tesla. Using T1 sequences, gadolinium DTPA showed increased signal intensity in the liver and in tumours, but this was significantly more marked in the tumour. On T1 spin-echo sequences, previously iso-intense lesions became visible after administration of contrast. On the other hand, contrast-enhanced lesions were less well seen on inversion recovery sequences because of a reduction in the contrast between tumour and liver tissue. The contrast between tumour and liver tissue was not improved by gadolinium DTPA in comparison with precontrast inversion recovery sequences and T2 spin-echo sequences. The perfusion of intra-hepatic tumours could be elucidated by magnetic resonance tomography after the administration of gadolinium DTPA.

Adult↗
PubMed1998

In vivo relaxation time measurements in the human placenta using echo planar imaging at 0.5 T.

This paper presents the first in vivo measurements of the nuclear magnetic resonance relaxation times T1 and T2 at 0.5 T in the human placenta from 20 weeks gestational age until term, in both normal and compromised pregnancies. T1 measurements were performed by using both an inversion recovery sequence and the Look-Locher echo planar imaging (EPI) sequence on a total of 41 women with normal pregnancies and 11 women with compromised pregnancies. T2 measurements were performed by using a spin-echo EPI sequence on 36 women with normal pregnancies and 14 women with compromised pregnancies. In normal pregnancies, both the T1 values measured with the inversion recovery sequence and the T2 values were found to decrease with gestational age, the linear regression results gave T1 = -9.1t + 1538 r2 = 0.23 p = 0.03. T2 = -4.0t + 338 r2=0.47 p =410(-6) where t is the gestational age in weeks, and T1 and T2 are the relaxation times in milliseconds. T1 values measured very rapidly with the Look-Locher EPI sequence, but, therefore, with a much lower signal-to-noise ratio, showed no significant trends. The T1 values measured in the abnormal group were significantly lower than those measured in the normal group. Four out of eight patients with compromised pregnancies had placental T1 values lying outside the 90% confidence limits for the normal population based about the regression line, significantly more than expected by chance (p = 0.005). Ten out of fourteen of the T2 measurements in the abnormal group were below the regression line established for the normal group, with 4 lying below the 90% confidence interval, although these trends were only just significant (p = 0.06 and p = 0.03).

Adult↗
PubMed1986

[Nuclear magnetic resonance imaging of the brainstem: evaluation of the normal structures and small lesions].

Nuclear magnetic resonance (NMR) imaging of the brainstem region from 12 asymptomatic individuals were reviewed in addition to these of 12 patients with various symptoms of small brainstem lesions. Abnormalities consisted of 3 cases of multiple sclerosis, 1 case of neuro-Behçet disease, 5 cases of infarction and hematoma and 3 cases of degenerative disease. NMR transverse imaging using inversion recovery sequence was able to locate many of the normal intra-axial brainstem nuclei, such as the periaqueductal gray matter, the red nucleus, the substantia nigra, the pontine nuclei, the pontine reticular nuclei, the facial nerve nucleus and so on in an about half of 12 asymptomatic individuals. The remarkable gray-white matter differentiation was obtained on NMR imaging using inversion recovery sequence and enabled the internal structures to be visualized within the brainstem. In addition, the midsagittal imaging provided an excellent demonstration of anatomical relationships of the brainstem and surrounding structures. In the diencephalic region, the mamillary body, the anterior commissure and the optic chiasma were also demonstrated on the midsagittal imaging. The lesions within the brainstem were vaguely shown on X-ray computed tomography in 6 of 12 patients but NMR imaging using inversion recovery or spin echo sequence provided more detailed data and revealed clear small lesions, such as the demyelinated plaques of multiple sclerosis and lacunar infarcts in 9 of 12 patients. Especially, in 2 of 3 multiple sclerosis patients, the plaques of the brainstem were definitely identified on NMR imaging only and the accurate localized lesion which was responsible for the facial myokymia or the Foville syndrome was identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Implementation and evaluation of a new pulse sequence for rapid acquisition of double inversion recovery images for simultaneous suppression of white matter and CSF.

We describe a fast double inversion recovery (DIR) imaging sequence that effectively attenuates signal from both white matter and cerebrospinal fluid (CSF). The pulse sequence uses a novel inversion/excitation scheme and fast spin-echo readout to maximize scan efficiency. The white matter/CSF suppressed images can be acquired from the entire brain in approximately 6 minutes. Evaluation of the fast DIR sequence on patients with multiple sclerosis (MS) demonstrates high lesion conspicuity.

Brain↗
PubMed2005

[Current imaging of nasal sinuses].

Depending on the problems, CT or MRI should be used in the differential diagnosis of conditions affecting the nasal sinuses. In particular, when chronic sinusitis is present, computed tomography should be performed before surgery to ascertain the condition of the bones. In most cases spiral CT with a decidedly lowered tube voltage and power (MAS product) is now used for this purpose. This means that the patient is exposed to about 70% less radiation than in other CT investigations. To avoid artefacts attributable to dental fillings, whenever possible the spiral should be tilted in such a way that the dental artefacts are not within the mass imaged. When an isotropic voxel is selected secondary reformatting is possible with no loss of quality. Diagnostic MRI should include both T1- and T2-weighted sequences before and after the administration of contrast agent. For the differential diagnosis of a space-occupying tumour coronal cuts about 2 mm apart are advised, whether the spiral or the conventional technique is used. A T2-weighted and fat-suppressed sequence or a STIR (short tau inversion recovery) sequence can also be helpful in the recognition and visualization of lymph nodes. If orbital involvement seems possible it is advisable to use a T1-weighted and fat-suppressed sequence in the coronal plane in addition to check this.

Facial Bones↗
PubMed2000

Trichloroethene reductive dehalogenase from Dehalococcoides ethenogenes: sequence of tceA and substrate range characterization.

The anaerobic bacterium Dehalococcoides ethenogenes is the only known organism that can completely dechlorinate tetrachloroethene or trichloroethene (TCE) to ethene via dehalorespiration. One of two corrinoid-containing enzymes responsible for this pathway, TCE reductive dehalogenase (TCE-RDase) catalyzes the dechlorination of TCE to ethene. TCE-RDase dehalogenated 1,2-dichloroethane and 1, 2-dibromoethane to ethene at rates of 7.5 and 30 micromol/min/mg, respectively, similar to the rates for TCE, cis-dichloroethene (DCE), and 1,1-DCE. A variety of other haloalkanes and haloalkenes containing three to five carbon atoms were dehalogenated at lower rates. The gene encoding TCE-RDase, tceA, was cloned and sequenced via an inverse PCR approach. Sequence comparisons of tceA to proteins in the public databases revealed weak sequence similarity confined to the C-terminal region, which contains the eight-iron ferredoxin cluster binding motif, (CXXCXXCXXXCP)(2). Direct N-terminal sequencing of the mature enzyme indicated that the first 42 amino acids constitute a signal sequence containing the twin-arginine motif, RRXFXK, associated with the Sec-independent membrane translocation system. This information coupled with membrane localization studies indicated that TCE-RDase is located on the exterior of the cytoplasmic membrane. Like the case for the two other RDases that have been cloned and sequenced, a small open reading frame, tceB, is proposed to be involved with membrane association of TCE-RDase and is predicted to be cotranscribed with tceA.

Amino Acid Sequence↗